A survey aircraft typically includes an aerial camera system that is arranged to capture ground images. Typically, the aerial camera system is mounted to an underside portion of the survey aircraft and ground images are captured as the survey aircraft moves along defined flight lines. The system is arranged to capture multiple images for each ground feature, which enables a photogrammetric solution, such as a bundle adjustment process, to be applied to the captured images in order to determine a best case solution for interior and exterior orientation information associated with each camera used and the images captured by each camera. The solution produced by the bundle adjustment process may then be used for further processing, such as 3D reconstruction, and to produce output product such as nadir and/or oblique photomaps and elevation datasets.
In order to improve the photogrammetric solution produced by the bundle adjustment process, the number of images taken for each ground feature must be increased, and typically this is achieved by capturing images more frequently so that the overlap between successively captured images is increased, by ensuring that sufficient overlap exists between adjacent flight lines, and by ensuring that images are taken from appropriate angles for each point on the ground.
In order to produce a good photogrammetric solution, a redundancy of about 10 is generally required, but with a relatively long associated focal length for each image and relatively large image overlaps, the ratio of distance between camera locations at image capture and distance to target (the ‘base-to-height’ ratio) is relatively small, which affects accuracy of the photogrammetric solution.
Productivity of an aerial camera system is determined according to the amount of ground area captured per hour at a given resolution. Therefore, since flying costs are primarily determined on an hourly rate, if a system captures more ground area per hour, then the cost per unit area decreases. Additionally, it is desirable to only capture the minimum amount of data required for a given area for it to be processed to the desired accuracy and output product requirements.
All aircraft operating in controlled airspace under Instrument Flight Rules are required to maintain a minimum separation from other aircraft at all times. This is accomplished by air traffic controllers monitoring position and velocity of all aircraft in the controlled airspace and providing directions to aircraft to ensure adequate separation for safe flight.
Airspace management jurisdictions around the world require that two separation conditions are achieved:                1. horizontal separation minima for aircraft flying at the same or similar altitude; and        2. vertical separation minima for aircraft at the same or similar latitude and longitude.        
Air traffic controllers apply separation standards to keep aircraft operating in controlled airspace and at airports with an operational control tower a minimum distance apart.
When two aircraft are separated by a distance that is less than a minimum separation distance defined by airspace classification, a loss of separation (LOS) situation is considered to exist, and air traffic controllers are prompted to intervene to instruct the pilots of one or both of the aircraft to take positive evasive action. A LOS does not necessarily mean that the two aircraft involved were at actual risk of colliding, rather that separation standards according to the relevant airspace classification were not maintained.
The parameters that may be changed to provide adequate separation between aircraft on converging flight paths include course, speed or altitude and changes to one or more of these parameters may be made to either or both aircraft.
Aerial survey aircraft are required to fly along predetermined flight lines which are generally parallel and at a fixed spacing. Minor deviations from the defined flight lines can be tolerated and image acquisition can continue. However, substantial deviation vertically or horizontally from the defined flight lines requires image acquisition to be suspended. The image acquisition can only recommence when the aircraft returns to the interrupted flight line at the location where the image acquisition was previously suspended.
Regularly Scheduled Passenger Transport (RPT) aircraft in most airspace jurisdictions have priority over other civilian aircraft when air traffic controllers make a decision about which of two aircraft on a converging flight path is to be diverted. Survey aircraft generally have the lowest priority compared to other airspace users. As a consequence, survey aircraft operating in controlled airspace will have a much greater likelihood of deviation from the respective planned flight lines than other air traffic.
However, deviation of a survey aircraft from planned flight lines causes significant loss of survey productivity because survey time is lost between suspension and recommencement of a survey flight and because of additional fuel required.